Levels of a small molecule found in humans and other primates are lower in the brains of depressed individuals, according to researchers at McGill University.

In a study published in the journal Nature Medicine, Dr. Gustavo Turecki, a professor at Montreal's McGill University, and his team discovered that the levels of a tiny molecule may provide a marker for depression and help detect individuals who are likely to respond to antidepressant treatment.

"Using samples from the Douglas Bell-Canada Brain Bank, we examined brain tissues from individuals who were depressed and compared them with brain tissues from psychiatrically healthy individuals,"says Turecki, who is also director of the McGill Group for Suicide Studies.

The team says it conducted several experiments that showed that antidepressants change the levels of the molecule.

"In our clinical trials with depressed individuals treated with citalopram, a commonly prescribed antidepressant, we found lower levels in depressed individuals compared to the non-depressed individuals before treatment," Turecki said. "Clearly, microRNA miR-1202 increased as the treatment worked and individuals no longer felt depressed."

Turecki says the discovery may provide "a potential target for the development of new and more effective antidepressant treatments."